1. Field of Invention
The present invention relates to image processing circuits and image processing methods suited to be used for electro-optical devices having electro-optical materials in which transmittances are changed according to an applied voltage. The present invention also relates to electro-optical apparatus using the circuits and/or the methods, and relates to electronic units.
2. Description of Related Art
Conventional electro-optical devices will be described below by taking an active-matrix liquid-crystal display device as an example by referring to FIG. 27. The liquid-crystal display device can be formed of a liquid-crystal display panel 100, a timing circuit 200, and an image-signal processing circuit 300.
The liquid-crystal display panel 100 is structured such that liquid crystal is sandwiched by a device substrate and an opposite substrate. The device substrate has a plurality of data lines and a plurality of scanning lines, and thin-film transistors (hereinafter called TFTs) disposed at the intersections thereof, serving as switching devices. Since liquid crystal has a characteristic in which its transmittance is changed according to an applied voltage, a desired gray scale can be displayed by controlling turning on and off of the TFTs.
The timing circuit 200 outputs timing signals used in sections. A D/A conversion circuit 301′ in the image-signal processing circuit 300 converts input image data D sent from an external unit, from a digital signal to an analog signal to output as an image signal VID. A phase-development circuit 302 ′ develops an input one-phase image signal VID to N-phase (N=6 in the figure) phase-development image signals and outputs them. The reason whey the image signal is developed to the N-phase signals is to extend a time in which an image signal is applied to TFTs to obtain a sufficient sampling time and a sufficient charging and discharging time of data signals sent through the data lines.
An amplification and inversion circuit 303′ inverts the polarities of the phase-development image signals in the following condition, and outputs output phase-development image signals VID1 to VID6 in which amplitude levels are adjusted according to the V-T characteristic (characteristic of transmittance against applied voltages), to the liquid-crystal display panel 100. The polarities of the output phase-development image signals are inverted such that the voltage levels of the signals are alternately inverted with the center voltages of the amplitudes of the signals being used as reference potentials.
The display performance of such a liquid-crystal display apparatus can be indicated by indexes such as a contrast ratio and a change in transmittance per gradation. The contrast ratio is a value obtained by dividing the maximum transmittance of the liquid crystal by the minimum transmittance. The larger the contrast ratio is, the larger the contrast of a displayed image is. The smaller the change in transmittance per gradation is, the higher-definition display is possible.